The invention relates to semiconductor fabrication techniques and in particular to improved manufacturing techniques for making ferroelectric actuator devices for ink jet printheads.
Ink jet printers continue to be improved as the technology for making the printheads continues to advance. New techniques are constantly being developed to provide low cost, highly reliable printers which approach the speed and print quality of laser printers. An added benefit of ink jet printers is that color images can be produced at a fraction of the cost of laser printers with as good or better quality than laser printers. All of the foregoing benefits exhibited by ink jet printers have also increased the competitiveness of suppliers to provide comparable printers in a more cost efficient manner than their competitors.
The primary components of the ink jet printhead are a semiconductor chip, a nozzle plate and a flexible circuit attached to the chip. The semiconductor chip is preferably made of silicon and contains various passivation layers, conductive metal layers, resistive layers, insulative layers and protective layers deposited on a device side thereof.
There are two primary types of ink jet printheads namely, thermal ink jet printheads and piezoelectric ink jet printheads. The piezoelectric printhead contains a thin film metal oxide which is widely used for many electromechanical applications. Examples of such electromechanical applications include surface acoustic wave devices, high frequency ultrasonic transducers and high speed ink jet printheads, just to name a few.
As electronic devices are improved, there is a need for an increased number of actuator devices such as the electromechanical devices described above which are more closely packed on a semiconductor substrate. Currently, wet etching of the metal oxide film is practiced, however, wet etching often results in undesirable undercutting of the oxide film and may leave etching residues which may contaminate the finished product. Also, hazardous materials such as hydrofluoric acid must be used. Accordingly, there continues to be a need for improved manufacturing techniques for microelectronic devices.
The invention provides a method for making thin film metal oxide actuator device. According to the method a first conductive layer is deposited on a silicon substrate. Next a thin film metal oxide layer is deposited on the first conductive layer. A negative photoresist material is applied to the metal oxide layer to provide a photoresist layer. The negative photoresist material contains components which are sufficient to form species which are reactive with the metal oxide layer during a dry etching process. The photoresist layer is patterned using light radiation energy and developed to provide one or more exposed portions of the metal oxide layer. The photoresist layer is etched with a reactive ion plasma sufficient to remove the photoresist layer and the metal oxide layer under the photoresist layer from the first conductive layer leaving the one or more exposed portions of metal oxide layer on the first conductive layer. A second conductive layer is attached to the metal oxide layer to provide a thin film metal oxide actuator device.
In another aspect the invention provides a reverse reactive ion etching process for making piezoelectric devices for ink jet printheads. The process includes
providing a silicon wafer,
depositing an insulating film layer on the silicon wafer,
depositing a metal conductive layer on the insulating film layer,
applying a metal oxide film to the conductive layer to provide a metal oxide layer,
spin-coating a negative photoresist material on the metal oxide layer,
drying or curing the photoresist material to provide a photoresist layer, the photoresist layer containing components which are sufficient to form species which are reactive with the metal oxide layer during a dry etch process,
exposing the photoresist layer to light radiation energy through a mask to provide a patterned photoresist layer,
developing the patterned photoresist layer to provide one or more exposed portions of the metal oxide layer, one or more remaining portions of photoresist layer covering the metal oxide layer,
dry etching the remaining portions of photoresist layer using a reactive plasma gas which is sufficient to react with the photoresist layer and metal oxide layer covered by the photoresist layer without substantially etching the exposed portions of metal oxide layer.
An advantage of the invention is the technique may be used with metal oxide films having thickness"" above about 1 micron without significantly increasing manufacturing time. The method may also be practiced without the use of wet chemical etching techniques which may providing undesirable undercutting of the metal oxide layers or may leave contaminants on the patterned metal oxide layers. Also, the methods of the invention are relatively safer to use since the methods avoid the use of hazardous chemicals such as hydrofluoric acid, buffered oxide etchant and the like and may provide products at lower operating costs.